1. Field of the Invention
This invention relates to an apparatus for measuring ionic activity of electrolytes contained in aqueous liquid samples such as body fluids. More particularly, this invention relates to a novel potentiometric electrolyte analyzer in which a slide-type ionic activity measuring device having ion-selective electrodes is transferred from a spotting section to a discharging section by way of a measuring section.
2. Description of the Prior Art
Measurement of ionic activity of an electrolyte ion, for example Na.sup.+, K.sup.+, Cl.sup.-, Ca.sup.2+, HCO.sub.3.sup.- or CO.sub.3.sup.2-, contained in such body fluids as whole blood, blood plasma, blood serum, and urine, has significant importance in clinical chemistry tests. For this measurement, an ionic activity measuring apparatus, i.e. a so-called electrolyte analyzer, has been used. Such techniques as flame analysis, coulometry and potentiometry are known for use in said analyzer.
In potentiometric measurement of ionic activity, an ionic activity measuring device having ion-selective electrodes is used. As such a device, a dry type device having film-like ion-selective electrodes has been disclosed, for example, in U.S. Pat. Nos. 4,053,381 and 4,437,970.
The basic structure of this ionic activity measuring device is that of a slide comprising at least one pair of solid state electrodes each of which has an ion-selective outermost layer and a porous bridge which can promote capillary action between two such ion-selective layers. The ionic activity of a specific ion contained in a sample solution can be determined by spotting a reference solution on one of the ion-selective layers and a sample solution on the other and then measuring the potential difference between the electrodes.
Accordingly, spotting of reference and sample solutions as well as measurement of potential difference must be conducted in an ionic activity analyzer in which this slide type device is used.
In the conventional analyzer used for this purpose, slide-type devices (hereinafter referred to as "a slide") are drawn out, one at a time, from a cassette of such slides, put into a thermostatic means after the spotting of one or more droplets of a sample and reference solutions thereon, and then transferred from said thermostatic means to a measuring section where the measurement of the potential difference is conducted. This apparatus is large in its horizontal plane due to the lateral arrangement of the cassette, the spotting section, the thermostatic means and the measuring section. Accordingly, there has been a demand for a smaller analyzer which is easy to use.